How ThermaDry3 works: Unique three-layer construction; first layer is Hydrolon terry which wicks moisture away from skin to keep you dry and comfortable. Perforated Hypolan blend middle layer is comfortable, cushioned and breathable, provides light compression which helps counteract tissue swelling. Durable nylon outer layer retains body's own heat, to naturally increase blood flow to damaged or painful joints and muscles to help encourage healing and pain relief. 12-1/2" long with tapered back for comfort and fit. Double oval over knee joint for warmth and padding. Open patella to relieve pressure on knee cap. Antimicrobial. Large fits 15-17" (38-43 cm) knee circumference.